This invention relates to a system for the production of duplicate copies of images. The invention is particularly concerned with duplicators of the type wherein copy sheets are supported on a cylinder and transferred to the sheets.
Highly satisfactory duplicating equipment is available for the production of copies with images formed on one side of the copy sheets. Such equipment can be reliably operated at highly satisfactory production rates.
Since copy sheet material of the type conventionally employed can readily accept images on both sides, it would be highly desirable to provide equipment suitable for transferring images to both sides of a copy sheet. This will provide clear savings in the amount of paper employed, additional savings in the amount of space occupied by the copies produced, savings in production time, and savings in cost of equipment.
Attempts have been made to produce copy sheets imaged on both sides (hereinafter referred to as "duplexing"). The use of separate presses located in tandem has been proposed, and although this represents a workable system, it is more costly due to the duplication of equipment involved. Paper handling considerations have also resulted in lower press speeds.
Perfector presses have also been employed for duplexing. Such presses utilize double master cylinders, blanket cylinders, ink systems, and dampening systems. More highly skilled operators and equipment expense make such presses undesirable.
Other proposals include the use of a large combination master and impression cylinder associated with a half-size blanket cylinder. In such an arrangement, the master cylinder places a first-side image onto the blanket cylinder whereby images are placed upon the sheets from the blanket cylinder and also from the impression section of the larger cylinder which includes a letter press or direct lithoplate. This system involves a lower production rate than other systems described.
Duplexing in copiers is accomplished by printing a desired number of first side sheets, storing the sheets, and then re-feeding them for receipt of a second side image. Reference is also made to Altmann U.S. Pat. No. 3,672,765 which discloses "on line" duplexing in photoconductive equipment.
Stonemetz Pat. No. 252,153 teaches a system for duplexing copies wherein a sheet is introduced between an impression cylinder and a type cylinder. In this system, the type cylinder carries two forms for transferring separate images, and a "blank" area is defined between the forms. The type cylinder makes one revolution while the smaller impression cylinder makes three revolutions. The copy sheet is printed on one side during a first revolution of the impression cylinder and discharged from the equipment. The impression cylinder makes an additional revolution while the "blank" area of the type cylinder passes, and the copy sheet is then re-fed, trailing edge first, for formation of the other image on the other side of the copy sheet during the third revolution of the impression cylinder.